Bonding of soft biological tissues by passing high frequency electric current therethrough

ABSTRACT

A technique for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are secured to the forceps for contacting the tissue portion. An electrical power source provides a high frequency electrical signal to the electrodes to be passed through the tissue portion. The electrical power source is controlled to provide the electrodes with one voltage signal during a first of two stages, and another voltage signal during a second of the two stages. During the first stage the voltage rises linearly. During the second stage, the voltage is stabilized and is modulated with a low frequency rectangular signal. A clamping means applies force with the forceps to compress the tissue at one level or at different levels during two time periods while the high frequency voltage is passed through the electrodes. The tissue impedance is measured as a function of time, with its minimal value being determined and stored. At an instant when the impedance reaches its minimal value, the linear rise of the high frequency voltage is stopped, and the voltage is stabilized at the attained level. After that the ratio of the tissue impedance to its minimal value is determined as a function of time. The passing of the high frequency voltage to the electrodes is stopped as soon as such ratio reaches a preset value, which is specific for each tissue being bonded. The material for making electrodes is selected so that the electrode may serve as an effective heat sink for conducting heat away from the tissue surface. The electrodes are dimensioned relative to the thickness of tissue in a compressed state.

BACKGROUND OF THE INVENTION

[0001] The present invention is directed to a technique for bonding softbiological tissue to close an incision therein and, in particular, toheating of the tissue with high frequency electric current incombination with compression of the tissue.

[0002] For purposes of the ensuing discussion, soft biological tissuewill be referred to just by the term “tissue” for reasons of simplicityand economy of space, and should be understood to mean any tissue otherthan bone, such as skin, organs, blood vessels and nerves. When tissueis injured, it must be repaired by re-joining the edges of tissue thathas been torn or cut. For example, when tissue is cut during a surgicaloperation, the incision(s) must be closed to complete the surgery. Infact, a tissue break (particularly in blood vessels) may also need to beclosed even during surgery, such as to provide hemostasis, namely tocontrol bleeding. Every cut, puncture or break in tissue due to anyreason is referred to herein generically as an “incision”.

[0003] Many techniques are known for closing an incision. Some of thesetechniques are suturing, clamping, stapling and gluing. These techniqueshave a number of well known disadvantages which include one or more ofthe following: leaving a foreign body in the tissue, pinching of tissuewhich can cause delayed healing and/or inflammation, allergic reaction,limited applicability, complexity of use, and the need for expensiveequipment.

[0004] Other techniques of connecting blood vessels use laser radiation,heated tools and the passing of high frequency current directly throughthe parts of tissue being connected. All the above mentioned methodsemploy the phenomenon of tissue albumen denaturation caused by heating.When the temperature exceeds 55° C. the denaturation causes albumencoagulation. The globular molecules of albumen become straightened andentangled among themselves. If two edges of tissue are connected andheated the entanglement of albumen molecules results in their bonding.The higher the temperature, the faster and better is the coagulation.However, at temperature exceeding 100° C. the tissue becomes dehydrated,its electric resistance increases, which leads to further temperaturerise and charring of the tissue.

[0005] Quite a number of research efforts have been published on lasertechniques in blood vessel surgery. Still this technique has not beenaccepted for general clinical use because of the technical complexity ofits utilization and because of inadequate surface energy release. As toemployment of high frequency current for heating tissue, the techniqueis widely used in surgery for hemostasis.

[0006] In tissue bonding, as with suturing for example, the separatedtissue edges must be rejoined to facilitate healing. The joint should berelatively strong, it must promote healing and minimize if not eliminateany problem which interferes with healing. However, the use of theexisting bipolar devices for connecting soft tissues other than walls ofcompressed blood vessels encounters insurmountable difficulties.Specifically, it has been difficult to correctly set the electricalsignal parameters to achieve such aims. This is due, at least in part,to the fact that tissue has an electrical resistance which can varywidely depending on many factors such as tissue structure and thicknessas well as the tool/tissue contact area which is not controlled in anyway. If too little current is applied, then the tissue joint can bespongy, weak and unreliable. On the other hand, if too much current isapplied, then the working surface of the electrode can stick to thetissue so that removal of the electrode causes bleeding and possibleinjury. Also, the tissue in the overly-heated zone can become desiccatedand charred. Therefore, such high frequency coagulative devices haveseen limited use for only hemostasis of blood vessels of relativelysmall diameter. These devices have not been used for replacing the wellknown above-mentioned means for bonding tissue (“bonding” is used in thesense of closing incisions to facilitate healing), such as suturing,stapling, etc. even though their use is not subject to theabove-mentioned disadvantages of such means for bonding tissue.

[0007] Two types of tools are used for high frequencyelectrocoagulation, namely mono-polar and bipolar. The discussion belowwill be limited solely to bipolar devices which provide an electriccurrent flow within the tissue volume clamped between the electrodes.

[0008] Use of bipolar devices to close incisions in tissue which must behealed will be appreciated as presenting quite a challenging taskbecause the amount of damaged tissue, such as due to charring or otherhealing-delaying effects, must be minimal and not very deep, and“overcoagulation” must be avoided. Prior art techniques have beenproposed to determine the degree of coagulation based on the electricalimpedance of the tissue. The relationship between electrical tissueimpedance over time and coagulation is described in the article“Automatically controlled bipolar electrocoagulation” by Vallfors andBergdahl, Neurosurgery Rev. 7 (1984), pp. 187-190. As energy is appliedto the tissue, the impedance decreases until it reaches a minimum value.If current continues to be applied, the authors describe impreciselythat the tissue begins to dry out due to the heat generated therein, andthe impedance rises. Unless the heating is stopped, severe tissue damagewill occur. Thus, the Vallfors and Bergdahl technique provides fordetermination of the instant of occurrence of the impedance minimum andthen stops the current flow a preset time thereafter. U.S. Pat. No.5,403,312 also utilizes this phenomenon to monitor the impedance, changein impedance and/or the rate of change in impedance to determine whetherit is within a normal range. However, these techniques are typicallyapplied to blood vessel coagulation. Usage of these techniques for othertypes of tissue creates severe difficulties due to the wide variation invalues of impedance which can be encountered due to, for example, tissuestructure, thickness, condition of the tissue and condition of the toolsurface.

SUMMARY OF THE INVENTION

[0009] One object of the present invention is to provide an improvedbipolar electrocoagulation technique for bonding tissue with heat energycreated by high frequency electrical current passed therethrough betweenelectrodes.

[0010] Another object of the invention is to prevent sticking of theelectrodes to the tissue.

[0011] A further object of the invention is to achieve a stronger bond.

[0012] Yet another object of the invention is to prevent burning oftissue in the bipolar electrode zone.

[0013] One other object of the invention is to provide a consistentlygood tissue bond regardless of differences in tissue structure andthickness.

[0014] Still another object of the invention is to bond tissue to closean incision quickly and reliably.

[0015] Another object of the invention is to bond tissue in a way whichpromotes fast healing.

[0016] A further object of the invention is to rely on measurement oftissue impedance to accurately control the degree of coagulation whichbonds the tissue for a wide variety of different tissues.

[0017] Yet another object of the invention is to design the electrodessuch that they can function as an effective heat sink for the heatedtissue with which they are in contact. Another object of the inventionis to design the electrodes to maintain uniformity in the area ofelectrode/tissue contact.

[0018] These and other objects are attained in accordance with oneaspect of the present invention directed to a method and apparatus forbonding soft biological tissue having an incision therein with forcepsadapted to grip a portion of the tissue on both sides of the incision.Electrodes are provided for contacting the tissue portion. An electricalpower source provides a high frequency electrical signal to theelectrodes to be passed through the tissue portion, and the electricalpower source is controlled to provide the electrodes with one voltagesignal during a first of two stages, and another voltage signal during asecond of the two stages.

[0019] Another aspect of the present invention is directed to a methodand apparatus for bonding soft biological tissue having an incisiontherein with forceps adapted to grip a portion of the tissue on bothsides of the incision. Electrodes are provided for contacting the tissueportion. An electrical power source provides a high frequency electricalsignal to the electrodes to be passed through the tissue portion, and aclamping means applies force with the forceps to compress the tissueportion, such force being set to different levels in two time periods,respectively, while the high frequency electrical signal is being passedthrough the tissue portion.

[0020] Another aspect of the present invention is directed to a methodand apparatus for bonding soft biological tissue having an incisiontherein with forceps adapted to grip a portion of the tissue on bothsides of the incision. Electrodes are provided for contacting the tissueportion. An electrical power source provides a high frequency electricalsignal to the electrodes to be passed through the tissue portion, with aconstant voltage level of the signal being provided during at least aportion of a time period when the high frequency electrical energy ispassed through the tissue portion, and the constant level beingmodulated by a low frequency signal.

[0021] Another aspect of the present invention is directed to a methodand apparatus for bonding soft biological tissue having an incisiontherein with forceps adapted to grip a portion of the tissue on bothsides of the incision. Electrodes are provided for contacting the tissueportion. An electrical power source provides a high frequency electricalsignal to the electrodes to be passed through the tissue portion. Theelectrodes are dimensioned relative to size of the tissue portion to bean effective heat sink for conducting heat away from the tissue andthereby prevent sticking of tissue to the electrodes.

[0022] Another aspect of the present invention is directed to a methodand apparatus for bonding soft biological tissue having an incisiontherein with forceps adapted to grip a portion of the tissue on bothsides of the incision. Electrodes are provided for contacting the tissueportion. An electrical power source provides an electrical signal to theelectrodes to be passed through the tissue portion. The impedancevariation in the tissue portion as a function of time, while theelectrical signal passes through the tissue portion, is predetermined toprovide a preselected impedance value. The impedance is measured toprovide a measured impedance signal as a function of time, while theelectrical signal passes through the tissue portion, and the electricalsignal is stopped from being passed through the tissue portion when avalue of the measured impedance signal reaches a preset impedance valuerelative to the preselected impedance value, with the preselectedimpedance value being specific in particular to the biological tissuebeing bonded.

[0023] Another aspect of the invention is directed to a method andapparatus for bonding soft biological tissue having an incision thereinwith forceps adapted to grip a portion of the tissue on both sides ofthe incision. Electrodes are provided which are adapted to contact thetissue portion in an electrode/tissue contact area. An electrical powersource provides a high frequency electrical signal to the electrodes tobe passed through the tissue portion. The electrodes are dimensionedrelative to size of the tissue portion to maintain uniformity in theelectrode/tissue contact area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a perspective view of a section of soft biologicaltissue with an incision therein prior to performing tissue bonding.

[0025]FIG. 2 shows the perspective view of FIG. 1 with tissue on bothsides of the incision being compressed between two electrodes to form agrasped flange of tissue in accordance with a first embodiment of theinvention.

[0026]FIG. 3 is an enlarged view of a portion of FIG. 2 prior to passingelectric current through the grasped flange of tissue.

[0027]FIG. 4 is similar to the view of FIG. 3, but with the graspedflange of tissue being compressed while electric current is applied tobond the tissue.

[0028]FIG. 5 is similar to the view of FIG. 4, but after the electrodeshave made a bond at one spot and then moved to another spot along theincision.

[0029]FIG. 6 is an enlarged perspective view of a lap-welded seam formedin bonding the tissue.

[0030]FIG. 7 is similar to the view of FIG. 6, but showing a spot-weldedseam.

[0031]FIG. 8 shows a cross section of a hollow organ with a flangedportion of tissue at the seam being grasped between the electrodes of asecond embodiment of the present invention.

[0032]FIG. 9 shows a perspective view of a third embodiment of theinvention.

[0033] FIGS. 10-12 are perspective views of a fourth embodiment of theinvention.

[0034]FIG. 13 shows a plot of volume power of heat release q at thetissue/tissue interface as a function of time, and of temperature as afunction of time for comparing continuous mode and pulsed mode of heatrelease, when the mean value of q_(o) applies to both modes.

[0035]FIG. 14 shows plots of temperature as a function of time at thecontact interface between an electrode and tissue (“contact” curve), andalso at a distance of 0.01 cm from such contact interface (“tissue”curve) for continuous mode heating and pulsed mode heating.

[0036]FIG. 15 is a schematic block diagram of a circuit for providing ahigh frequency electrical signal to the electrodes in accordance withthe invention.

[0037]FIG. 16 is a perspective view of a forceps tool for performingbonding in accordance with the present invention.

[0038]FIG. 17 shows a-cross-section taken along line 17-17 of FIG. 16.

[0039]FIG. 18 is an electromagnetic version of the forceps shown in FIG.16.

[0040]FIG. 19 is a cross-section taken along line 19-19 of FIG. 18.

[0041]FIG. 20 is a graph of tissue impedance over time for tissue beingheated by high frequency current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042]FIG. 1 shows tissue 2 with an incision 4 formed therein. Incision4 could have been formed as part of some surgery done on a patient, orit could be an injury due to some type of trauma. The incision can be acut in the skin or in a wall of an organ, or the organ itself, e.g. ablood vessel or nerve. In any case, the incision must be closed bybonding, or joining, the edges of tissue 5 and 6 on either side of theincision to each other.

[0043] In accordance with the present invention, the edges 5, 6 at end 3of the incision are gripped and raised by pincers (not shown) to formtissue portion 10 in the form of a flange. This is depicted in FIG. 1. Aforceps tool (referred to herein as a forceps) is provided in the formof any instrument capable of gripping the tissue and selectively addinga clamping force under manual control. Various forceps designs are wellknown. Typically they include a pair of arms with opposed ends betweenwhich the tissue can be gripped. Forceps arranged in accordance with theinvention are described below. For now it is sufficient to know that theforceps include clamp arms 8. As shown in FIG. 2, electrodes 11 aresecured at the opposed ends of clamp arms 8 to grip portion 10 of thetissue therebetween. To grip the tissue, sufficient force is used tojust retain the tissue between electrodes 11 so that it does not slipout of position. The gripped tissue is not significantly compressed.

[0044] Clamp arms 8 are entirely metallic or only the tissue-graspingtip is metallic to form electrodes 11. Thus, the tissue portion, orflange, 10 is in contact with two electrodes 11 on its sides. Currentfrom a high frequency (“HF”) electric power source 12 is provided toelectrodes 11 by conductor wires 14. This creates a bipolar electrodearrangement so that electric current generated between electrodes 11passes through flange 10 of tissue 2.

[0045] Electrodes 11 are initially pressed toward each other to engageflange 10 with a minimal pressure P sufficient to grip flange 10, asexplained above. However, the tissue need not yet be compressed to anysubstantial degree, as shown in FIG. 3. In contrast, by virtue of theextent to which FIG. 4 shows that the electrodes sink into the tissue atportion 16, pressure P has been increased to significantly compress, orclamp, the flange 10. Then, an HF signal is applied to electrodes 11from source 12.

[0046] It must be realized that the zone 7 between the electrodes 11contains an electrical impedance. It should be noted that heat isgenerated by current flow through tissue due to its resistance.Therefore, resistance is used below when the invention is explained interms of heat due to current flow, although it is understood that whenmeasurements are made, the measured parameter is impedance. Tissueresistance has several components. One component, called thetissue/tissue component, is the resistance between the opposed edges 5,6 of tissue on either side of incision 2. Another component, called thebulk tissue resistance component, is the resistance of that portion oftissue 2 which is grasped between the electrodes 11 in the form offlange 10. A further component, called the electrode/tissue component,is the contact area between the electrodes 11 and the tissue of flange10.

[0047] Tissue between electrodes 11 is heated because of heat generatedby electric current flowing through the tissue due to the electricresistance of the tissue in zone 7. Due to the presence of manyvariables, it is difficult if not impossible to accurately predict themagnitude of the resistance components nor how heat will spreadtherethrough and be released therefrom.

[0048] The edges 5, 6 are preferably clamped with a preset pressure of acertain experimentally determined magnitude depending on tissuestructure and thickness, and the bonding current is passed through theseclamped edges. One benefit of such clamping (others are presented below)is that it serves to form better contact areas by conforming the opposedsurfaces to each other. Rather than having a random number of pointcontacts between, say, edges 5 and 6, this approach creates a firmsurface contact with more predictable electric contact resistancesbetween the electrodes and tissue, and between tissue and tissue. As aresult, it stabilizes the heat generated by electric current due tothese resistance components. At the same time, the clamping of thetissue edges by a preset pressure during the process of heating allowsdensification of the straightening and entangling albumin molecules inthe tissue/tissue contact area to thereby improve the strength of thebond created with this bipolar heating as compared to what the bondstrength would be without such clamping.

[0049] One advantage of using alternating current, particularly of highfrequency, is as follows. While direct current traverses the tissueedges, electrolytic ions move in the direction of the electric poles inaccordance with their polarity. A sufficient concentration of these ionson the locally heated tissue ends may produce an electrolytic effectwhich causes a chemical burn of the tissue. By using alternating currentfor heating the tissue edges, the electrolyte ions do not move in thetissue just in one direction but, rather, they change their direction ofmovement with the changing polarity, so that the ions oscillate abouttheir quiescent state. The amplitude of these oscillations variesinversely with the frequency of alternating current. Thus, a higherfrequency of alternating current will result in lower amplitude of theseoscillations, thereby reducing the electrolytic effect.

[0050] Thus, a strong and effective bond between the tissue edges isachieved by means of first clamping such edges together with a presetpressure having a level depending on tissue structure and thickness, andthen passing a high frequency alternating current through these clampededges sufficient to heat the tissue in the current conductive zone 7.

[0051] A further feature aimed at overcoming the above-describeddrawbacks of bipolar devices, and in accordance with a principal aspectof the present invention, is to apply heat in a two-stage thermal cycleto the tissue being bonded in zone 7. The first stage stabilizes thebulk tissue resistance component. Then, in the second stage, a good bondis created by virtue of being able to provide stable, predictable tissueheating and to produce satisfactory heat removal from theelectrode/tissue interface. As explained below, this contributes tocreating a defectless and reliable bond while avoiding sticking of thetissue to the electrodes.

[0052] It is advisable that pressure P applied to flange 10 by the arms8 through electrodes 11 does not exceed 15 N/mm² and be no lower than0.5 N/mm². The wide range of pressure values is explained by the factthat soft tissues have widely varying thicknesses and structures(compare, for example, tissues of a nerve, stomach, liver, skin, etc.).The exceeding of the maximal acceptable pressure value P for aparticular type of tissue with a certain thickness δ has beenexperimentally shown to cause a considerable volumetric deformation oftissue in the bonding zone 7 with the result that it increases the timerequired to heal the tissue after bonding. The decrease of pressurebelow a minimal acceptable value for a certain type of tissue with athickness δ leads to deterioration of the joint reliability because ofunstable electric resistance components (as discussed above) and heatdevelopment, and because insufficient entanglement among albuminmolecules is created in the tissue/tissue contact area. It also leads tostrong sticking of the contacting surface of the welding electrodes tothe tissue surface because of the increased value of electric contactresistances and poorer heat release in the electrode/tissue contactarea.

[0053] The time duration T during which current is passed through thetissue is within the range of 0.1 to 3.0 seconds depending on tissuethickness and structure. The relation between heating time and tissuethickness is derived from Fourier's Law of Heat Conduction (see B.Paton, V. Lebedev, “Electric equipment for flash-butt welding. Elementsof the theory.”, Mashinostroyeniye Publishers, Moscow 1969, pages 38-45)in accordance with which a dimensionless number II is a constant value.${II} = \frac{aT}{\delta^{2}}$

[0054] where

[0055] a=λ/c·γ is biological tissue temperature conductivity;

[0056] λ is specific heat conductivity,

[0057] c is heat capacity,

[0058] γ is tissue density, and

[0059] δ is tissue thickness in a compressed state.

[0060] Since II is a constant, the heating duration time T should beproportionate to the tissue thickness squared. Exceeding the maximumlimiting value of time T for a particular type of tissue with a certainthickness δ is related, as has been experimentally shown, to tissueoverheating which slows down the healing process and increases theprobability of electrode adhesion to tissue. Decreasing time T below theminimum allowable value leads, as has been experimentally shown, toinsufficient coagulation of albumin in the tissue and poorer bondreliability.

[0061] As pointed out above, one key aspect of the invention is to applya two-stage thermal cycle. Thus, time T is divided into portions T₁ andT₂. During the first stage T₁, voltage on the electrodes is raised froma starting value of 0 to a preset maximum level. The selection of thevoltage rise rate of the power source is based on prior experience andtaking into account the type of tissue and the thickness of tissue. Therate of voltage increase is preferably the same throughout first stageT₁ so that it appears as a straight line, or ramp, on a graph of voltagevs. time. The maximum value reached in first stage T₁ is preferably thevoltage used for second stage T₂. During stage T₂, the applied voltageis constant.

[0062] A rate of voltage rise which is too slow may result in expandingthe area of the heated tissue beyond the borders of zone 7 and therebyreduce the heating localization, and this will eventually result inincreasing the time required for healing. A rate of voltage rise whichis too fast may cause nonuniformity in tissue heating which impairs thestability of bonding formation conditions.

[0063] The first stage of the thermal cycle is effective for the thermaland mechanical development of better contact areas and forming aconductive path through which the larger portion of current flows.During this first stage, pressure P is applied to firmly clamp theopposed tissue edges against each other to create surface/surface ratherthan point/point contact areas.

[0064] For the first stage of the thermal cycle, voltage is increased ata given rate during time T₁. Then, a steady voltage level is applied fortime T₂ of the second stage which commences immediately after completionof the first stage. This second stage is the bonding part of the thermalcycle, which provides straightening, interlacing and infiltration ofalbumin molecules in the current conductive zone 7 (FIG. 3) to reliablybond the edges 5 and 6 clamped (FIG. 4) between electrodes 11.

[0065] Good heat transfer is achieved by the first stage because itcreates extra contact areas in the current conductive zone 7 whichprovide fast heat removal of heat due to the electrode/tissue resistancecomponent. This reduces the probability of adherence, or sticking, ofthe electrode work surface to the tissue edges.

[0066] After bonding of the edges at a first spot 20 (see FIG. 5) alongseam 9, the electrodes 11 are returned to their initial, separatedposition (which is shown in FIG. 1). To make the second and thesubsequent bonded spots on the seam 9 of the flanged edges 5 and 6 oftissue 2, the thermal cycle described hereinabove is repeated to producespots 20 ₁, 20 ₂ . . . 20 _(n) (see FIGS. 5-7). If it is necessary toprovide a hermetically sealed joint of tissue, step Lt by whichelectrodes 11 are moved along the seam (FIG. 6) must be selected in sucha manner that the previously bonded spot (for instance spot 20) isoverlapping the following spot 20 by 10 to 30% of its length Dt (i.e.Lt<Dt). If tight sealing is not required, step Lt (FIG. 7) is selected(i.e. Lt>Dt) in accordance with other requirements (for instancestrength, external appearance of the joint, etc.).

[0067]FIG. 8 shows a hollow tissue 2, such as a blood vessel, which hasbeen severed. The two ends 5′ and 6′ are joined to form a circularflange 10′, and electrodes 11 at the ends of arms 8 clamp the tissuetherebetween at one point along the periphery of flange 10′. As currentis passed between the electrodes through the tissue, bond 20 is made atone point along seam 9. Electrodes 11 can then be moved around theperiphery to form bond 20 ₁, and so on around the entire circumferenceof circular flange 10′.

[0068] As shown in the embodiment of FIG. 9, clamping arms 8 a areprovided with electrodes 11 a having holes 23 in the bottom and sidewhich engage the tissue. Electrodes 11 a are hollow and have aconnection (not shown) to a vacuum source (not shown). When vacuum isapplied to electrodes 11 a they grip the tissue so that it can be heldsecurely and properly positioned for having current pass effectivelytherethrough to carry out the above-described thermal cycle.

[0069] FIGS. 10-12 show a fourth embodiment of the invention which isdesigned to bond the entire periphery of the hollow tissue, such as ablood vessel, discussed above in connection with FIG. 8. The bloodvessel is shown in FIG. 10 after it has been cut into parts 30 and 32.Tissue part 30 is inserted into semicircular electrode sleeve 34attached to the end of arm 36. Similarly, tissue part 32 is insertedinto semicircular electrode sleeve 38 attached to the end of arm 40. Theaxes of sleeves 34 and 38 are aligned along line 42, and tissue ends 30a and 32 a face each other. As shown in FIG. 11, another semicircularelectrode sleeve 35 is placed onto its mate 34 to encircle tissue part30 therebetween. Electrode 35 is attached to the end of arm 37.Likewise, semicircular electrode sleeve 39 is placed onto its mate 38 toenclose tissue part 32 therebetween. Electrode 39 is attached to the endof arm 41. These various parts can be part of a tool (not shown), thedetails of which are apparent to one with ordinary skill in the artbased on the explanations and descriptions provided herein.

[0070] Tissue end 30 a is folded back on itself by turning it inside outwith pincers to form flange 44. The flange 44 is pulled up overelectrodes 34, 35 to be tight against the ends of the electrodes. Also,in order for tissue part 30 to be secured onto the electrodes, aperipheral collar 45 (FIG. 11) is formed onto which the edge of end 30 ais placed. In similar fashion, electrodes 38 and 39 have peripheralcollar 46 formed therein. End 32 a is pulled tightly over collar 46 toform flange 48.

[0071] As shown in FIG. 12, output terminals 12 a and 12 b of the powersource are connected to the above-described arrangement. Morespecifically, current from terminal 12 a is provided via conductionwires 14 a and 14 b and arms 36, 37 to electrodes 34, 35 respectively.Of course, current could be supplied directly to the electrodes byattaching wires 14 a and 14 b thereto. Current is provided in likefashion to electrodes 38 and 39, respectively, via wires 14 c and 14 d,and arms 40 and 41.

[0072] Assembly 50 for holding tissue part 30 and assembly 52 forholding tissue part 32 are at the tips of pincers or forceps (notshown), and these are brought toward each other by moving one or bothalong line 42 in order to compress flanges 44 and 48 along the entireperiphery formed by the electrodes 34, 35, 38 and 39. Pressure andcurrent are applied in the same manner as described above with respectto FIGS. 1-5, and the result is a circular seam 54 produced by a singlethermal cycle. After the bond is formed, flanges 44 and 48 are removedwith pincers from the electrodes. The electrode mates are then separatedto release the now re-joined hollow tissue parts 30 and 32.

[0073] The periodic variation (i.e. modulation) of the heat intensitygenerated in the tissue promotes the creation of a bond. Sharptemperature rises separated by intervals increase the duration of thetissue being exposed to a stressed state which should promote therupture of the cellular membranes (why this is relevant is explainedbelow) and aids in formation of a solid bond. Also, the modulation ofheat with application of a constant average power results in an increaseof the time that the internal tissue layers i.e. between but spaced fromelectrodes 11, are exposed to a high temperature. Not only thetemperature exceeding a certain limit but also the duration of tissueexposure to that temperature are important for the coagulation processwith energy absorption needed to form a bond. In this connection,modulation of heat with application of a constant average power leads toa positive result. In order to explain this assertion, consider a“temperature pulse” variation in a linear approximation with repeatedshort-duration, or pulsed, heating of (or energy release into) tissue isapplied. Q = ∫₀^(T)θt  

[0074] where

[0075] Q is pulse

[0076] t is time,

[0077] T is duration of time during which current is passed through thetissue, and

[0078] Θ is temperature.

[0079] The calculations show that temperature increase is effective fora larger part of the tissue volume between the electrodes when pulsedheating is applied in comparison with when continuous heating isapplied. Heat conduction in the electrode affects the heating of thelayers immediately adjacent to the electrode. Let us assume that thetissue heating is pulsed with N cycles (e.g. N=4 in FIG. 13), each cyclehaving a time duration τ. High frequency current passes through thetissue during time t_(u) in every such cycle of duration τ. The volumepower of heat generated is q. Let us compare tissue heating under thesepulsed mode conditions with continuous mode tissue heating at per-volumepower q_(o). The average volume power in the pulsed heating of tissue isq_(o), the same as in the continuous mode, i.e.

q·t _(u) ·N=q _(o) ·T

[0080] where:$q = {{q_{o}\frac{T}{t_{u}N}} = {q_{o}\frac{\tau}{t_{u}}}}$

[0081] As shown in FIG. 13, in the continuous mode, tissue temperatureincreases in proportion to the time duration that current is applied, asper $\theta = \frac{q_{o}T}{c\quad \gamma}$

[0082] where c is heat capacity, and

[0083] γ is density.

[0084] In the pulsed mode, the tissue temperature also increases as thehigh frequency current flows during time t_(u), but the increase occursat a steeper rate since q>q_(o). During the time of no current flow, thetemperature remains constant until the beginning of the next heatingcycle due to low conductivity of tissue (FIG. 13). By the end of theheating process in the continuous mode “temperature pulse”,

Q _(H) =q _(o) T ² /cγ

[0085] whereas in the pulsed mode:$Q_{n} = {\frac{T^{2}}{c\quad \gamma}\left\lbrack {1 + \frac{1 - \frac{t_{u}}{\tau}}{N}} \right\rbrack}$

[0086] The difference${Q_{n} - Q_{H}} = {\frac{q_{0}T^{2}}{c\quad \gamma} \cdot \frac{1 - \frac{t_{u}}{\tau}}{N}}$

[0087] produces an additional effect as to tissue bonding. Moreover, thetemperature at the electrode-tissue contact surfaces remains practicallythe same for both modes (FIG. 14).

[0088] It follows from the above that in the pulsed mode the requiredbonding can be achieved at lower per-volume power than in the continuousmode, and consequently at a lower temperature in the electrode-tissuecontact zone. The tissue adhesion to the electrodes will thus be lower.This is one advantage of using the pulsed mode heating.

[0089] It follows from the above formula for Q_(n)−Q_(H) that the loweris t_(u)/τ, the higher must be q (see FIG. 13) to maintain the sameq_(o), and the longer is the time duration that tissue remains under theincreased temperature conditions. There must be optimal values fort_(u)/τ and N. Values of t_(u)/τ=0.5 and 4≦N≦6 were used to provide highfrequency current modulated with square pulses of lower frequency (4 to6 Hz). The obtained experimental results were positive.

[0090] The purpose of low frequency pulse modulation is explainedsuccinctly as follows. Initially, it may seem that during the break incurrent flow (i.e. during τ−t_(u)) the temperature in the tissue/tissuecontact area should decrease and, therefore, the probability of a goodbond will be reduced. Actually, the effect of low frequency modulationresults in increased exposure of tissue to high temperature treatmentbecause the tissue at the tissue/tissue interface receives the increasedenergy generated by the HF current as well as retaining the heat for alonger time because it is relatively distant from the heat sink effectof the electrodes. Thus, the low frequency modulation effect isexplained by a longer duration of tissue exposure to high temperaturewhich allows a decrease in the total energy needed for forming the bondand consequently reduces the adhesion of tissue to the electrodes. Anincrease in the modulation frequency (i.e. the value of N) reduces thiseffect to zero.

[0091] Peculiarities of Tissue as an Element of an Electrical Circuit

[0092] Any biological tissue includes cells and inter-cellular fluid.The latter contains a small quantity of albumin, most of it concentratedin protoplasm. The cells and inter-cellular fluid are separated withhigh electrical resistance membranes. The current conductivityproperties of tissue at low voltage are caused mainly by motion ofinter-cellular fluid ions. In an alternating electric field, ions andpolar molecules of protoplasm contribute to conductivity properties. TheAC current caused by periodic alignment of dipoles induced by thealternating electric field is called a bias current. The higher is thefrequency, the higher is the bias current in the membranes andcorrespondingly in protoplasm.

[0093] The generation of a monolithic connection bonding together thetissue edges may only be possible due to, firstly, rupture of cellularmembranes and, secondly, coalescence of cellular protoplasm. The ruptureof the cellular membranes due to current flow therethrough is a gradualprocess although it has a somewhat chain-reaction-like character. Suchrupture can also be accomplished with tissue deformation caused bypressure applied to the tissue with the electrodes.

[0094] An electrical rupture of a cellular membrane can occur byexposure to heating, but only under the condition of certaincombinations of electric field voltage and temperature. The electricalrupture starts with the cells having the weakest membranes. The electricfield voltage drops in the cells with ruptured membranes due todecreased resistance therein, and voltage correspondingly increases inthe cells with as yet unpunctured membranes. The rupture probability ofthe neighboring cells thus increases, and so on.

[0095] Such a phenomenon of tissue resistivity decrease due to ruptureof the cellular membranes is corroborated by measurements. It ischaracteristic that the higher the voltage which is applied to theelectrodes, the sharper is the resistivity drop. One more circumstanceworthy of being pointed out is that an increase of the clamped tissuevolume results in delaying the tissue resistivity drop which occurs dueto rupture of the cells. A statement that these relationships areprecise would not be accurate. Differences in tissue structure also hasa significant impact on the process.

[0096] As regards use of tissue deformation caused by pressure appliedwith the electrodes, under such pressure the compressed tissue stretchesin the direction perpendicular to the electrode axis. This may cause apurely mechanical rupture of some membranes. After electrical rupturebegins, such mechanical rupture becomes more probable.

[0097] A constant difference in potential between the electrodes causestissue deformation to be accompanied by the increase in electrical fieldstrength on membranes that are still intact which, in turn, facilitatesrupture of those membranes.

[0098] Thus, the initial heating of tissue during the first stage of thethermal cycle serves to create a conductivity path through the tissue toenable current flow with a relatively uniform current densityprincipally confined to the tissue clamped between the electrodes.

[0099] Tissue heating during the second stage of the thermal cycle isaccompanied by structural changes in the albumin, namely globularmolecules straighten out and become intertwined among themselves, whichcreate a decrease in tissue conductivity.

[0100] During the second stage it is preferable to increase the clampingforce applied by the electrodes for the purpose of creating the bestconditions for creating a bond. It has been experimentally proven thatan increased force applied on the electrodes in the second stage resultsat least in 10-20% increased strength of the tissue bond.

[0101] After the second stage is completed, it is preferable to continueapplying the clamping force to the bonded tissue for a certain time. Itis not so much the duration of this additional clamping time that isimportant but, rather, the sequence of current shut-off after the secondstage followed by removal of clamping pressure.

[0102] Peculiarities of Frequency Selection

[0103] Frequencies selected for electrical surgery purposes inaccordance with this invention are in the range of 50 to 2000 kHz. Thisfrequency range is not perceived by the nervous system of humans andanimals.

[0104] Experiments were conducted within a wide frequency range to testthe strength of the bond and determine the dispersion, or variance, ofthe results. The experiments showed, for example, that 50 kHz is theoptimal frequency for bonding an incision in a rat stomach. Thisfrequency provides the strongest bonding and the closest to minimaldispersion. The 50 kHz frequency is well tolerated by a live organismand its use is possible. On the other hand, for a very thin tissue, likethe one wrapped around a nerve stem, a frequency of 1000-1400 kHz ismore appropriate. It was concluded from these experiments that carefulselection of frequency depending on the thickness and type of tissue isrequired.

[0105] Automatic Control

[0106] The preferred approach for usage of electrocoagulant bonding inpractical surgery is a computerized system. A surgeon will have to inputinformation into a computer, such as the kind of animal, its age, organto be operated, and tissue type. This data would enable the computer tofind in its memory a proper prestored bonding mode close to the optimal(as explained below). There also should be included an optional featureenabling the surgeon to make additional corrections in the bonding modeduring surgery, as well as for the computer to make certain adjustments,taking into account specific peculiarities pertinent to certain animalsand potential interferences (disturbances) resulting from actualconditions of the surgery.

[0107] The following are possible disturbances affecting the bondingprocess:

[0108] a) contamination of working surfaces of electrodes,

[0109] b) variation of the tissue thickness,

[0110] c) variation of the clamping force of electrodes,

[0111] d) by-passing the current through adjacent tissue areas,

[0112] e) inhomogeneity of tissue in the bonded area,

[0113] f) excessive temperature of electrodes,

[0114] g) inhomogeneity of tissue surface, e.g. dry, damp, traces ofblood, etc.

[0115] The automatic control system which relies on feedback circuitsresponsive to such disturbances should vary the heating mode in such amanner that their effect is minimized. Contamination of the work surfaceof the electrodes should be detected in the beginning of the bondingbefore any serious damage is done. For that purpose, a short durationhigh frequency probing pulse is fed through the tissue portion 10 fordetermination of its impedance. Should it be higher than thepredetermined level for the type of tissue being bonded, the surgeonneeds to be so informed by a signal so that the surgical tool is cleanedor replaced.

[0116] Shorting of the electrodes through the tissue clampedtherebetween may also be detected by a probing pulse. If the impedancemeasurement is lower than a certain predetermined level, the bondingprocess should be immediately discontinued and the surgeon notified.

[0117] Variation of the tissue thickness can be detected by way ofmeasuring mechanical strain on the forceps cantilevers, or arms,(described below) and comparing it with the distance of the latter'stravel. Direct measurements are also possible but they would complicatea simple tool like forceps and are hardly acceptable. As has alreadybeen pointed out, the tissue thickness affects the rate of impedancedrop to its minimal value, provided all other factors remain unchanged.This factor is used for computerized control of the bonding process (asexplained below).

[0118] Disturbances caused by previously bonded spots adjacent the zone7 being bonded are not so significant, provided the voltage fed to theelectrodes 11 has been held constant. Shunting of the tool's currentthrough other tissue parts should be prevented by way of reliableinsulation covering all surfaces of materials that conduct electricity,except the work surface of the electrodes. It is more difficult tocreate a control system responding to the (e) type of disturbance. Thechange of tissue impedance caused by its inhomogeneity may not require achange of power or energy for bonding. In this case, indicationsindirectly reflecting the bonding process should be sought after, asdiscussed below.

[0119] Overheating of the electrodes can be eliminated by way of havingmade provisions in the computer program for limiting the amount of timeand the rate of tool operation. This is done by generating an audibleand/or visual alarm signal which notifies the surgeon that the toolneeds cooling off.

[0120] The tissue surface condition (g) should be initially checked andthen monitored by the surgeon. Nonetheless, effects of thesedisturbances should be at least partially monitored by the controlsystem, as pointed out above.

[0121] System Without Feedback

[0122] This is the most unsophisticated system. The bonding mode isdetermined by the rate of high frequency voltage rise in the firststage, voltage heating time duration in the second stage and clampingpressure. Each of these values is set up by the operator or recoveredfrom computer memory and applied during the operation.

[0123] The system does not respond to any of the above-listeddisturbances.

[0124] System with Stabilization of the Output High Frequency Voltage

[0125] This embodiment differs from the one immediately above byproviding a more accurate reproduction of the intended bonding modedespite disturbances (a) through (d). The system should respond to thecondition of the electrode work surfaces and to short circuits whicharise during the tool's operation cycle, both before the bonding andduring tissue heating. The system also informs the operator of itsdiagnosis results.

[0126] As described above, one feature of the invention is to use atwo-stage thermal cycle in which during the first stage the voltageincreases at a predetermined rate for a certain time, and during thesecond stage a continuous voltage is applied to the tissue at themaximum voltage level reached in the first stage. As also describedabove, tissue impedance is used in accordance with another feature ofthe invention to stop current flow in order to prevent excessivecoagulation and resultant tissue damage.

[0127] These two features are combined as follows. The first stagecontinues until occurrence of the minimum impedance Zo is determined(see below and FIG. 20). Upon that (i.e. at time t′₂ for impedance curveZ₂) further rise of the voltage is halted and the voltage level whichhas been reached is stabilized for use in the second stage. The secondstage is then applied until the preset value of Z/Zo (see below) isreached (e.g. at time t₂), at which time further current flow isstopped.

[0128] Automatic Control System Employing Relative Value of TissueImpedance

[0129] As explained above in connection with the article authored byVallfors and Bergdahl, prior art techniques rely on determining absolutevalues of impedance Z or of its change with time dZ/dt and their use forautomatic control with feedback. However, these values can vary greatlyfrom tissue to tissue because impedance is affected by many variables.If these prior art techniques are restricted to the same type of tissue,such as blood vessels, they can be valuable. However, significantinaccuracies, and resultant tissue damage, can occur when valuespredetermined for one type of tissue are applied to control current flowthrough another type of tissue.

[0130] Accordingly, the invention utilizes relative values based on therate of Z/Zo, where Zo is the minimum impedance value determined eachtime bonding is performed on a particular type of tissue, and Z is thepresent value of impedance being measured as current is applied to suchtype of tissue. Thus, the minimum point Zo₁ on the impedance curve Z₁(FIG. 20) is calculated by well known means e.g. utilizing computer 70described below. When the ratio Z/Zo₁ reaches a preset value, furtherheating is stopped by breaking the current flow, e.g. at time t₁. Forthe next bonding process on another type of tissue, impedance curve Z₂is processed in the same way with the result that current flow isstopped at time t₂. The use of this approach is advisable in combinationwith the embodiment which provides stabilization of a high frequencyoutput voltage (see below).

[0131] System with Automatic Setting of High Frequency Voltage

[0132] This system responds to the (b) type of disturbance which iscaused by variation of the tissue thickness. As has been pointed outabove, a current conducting path is created in the clamped flange oftissue by way of the rupturing cellular membranes. An increase in tissuethickness results in a longer time being required for the formation of acurrent conducting channel, and vice versa. If in the first stage of thethermal cycle the high frequency voltage is increased at the rate ofapproximately 300-400 V/sec, the tissue impedance will drop smoothlyuntil it reaches a certain minimal value Zo. As soon as the minimumvalue of tissue impedance Zo is reached, the high frequency voltagebecomes stabilized at the particular level which has been reached. Thatvoltage level is then applied in the second stage.

[0133] Thus, the increase and decrease in tissue thickness causes thevoltage to be set at higher values and at lower values, respectively,for the second stage.

[0134] Current cutoff to stop the tissue heating is achieved by thecontrol system in response to the relative value of tissue impedanceZ/Zo, as explained above.

[0135] It is important to select the correct rate of voltage rise. Forexample, it has been noticed that for stomach and intestinal tissues, arate of voltage rise exceeding 400 V/sec is not advisable due to anexcessively fast formation of the conductive path. The system mustprovide monitoring to inform the surgeon about the correspondencebetween actual voltage parameters and the voltage parameters preset inthe computer.

[0136] Circuitry for Electrical High Frequency Bonding

[0137]FIG. 15 shows the circuitry which produces the high frequencysignal provided to the electrodes 11.

[0138] Signal generator 60 converts AC mains voltage from power source78 to the signal which is provided to electrodes 11 via cable 80 andarms 8 which are mounted in sleeve 100. Power supply 61 receives the ACmains voltage and provides a regulated, isolated, filtered DC voltage of100 volts. Voltage regulator 62 receives the output of power supply 61and provides an output voltage that can be controlled to any levelbetween 0 and 100 volts. Inverter 64 transforms the DC voltage itreceives from voltage regulator 62 to an alternating signal with acontrolled frequency. The output of inverter 64 is coupled to electrodes11.

[0139] Current sensor 63 and voltage sensor 65 measure the current andvoltage, respectively, at the output of voltage regulator 62, and thesemeasurements are provided to computer control system 70. Computercontrol system 70 includes a suitable microprocessor 72 operating inconjunction with other standard and well known system components (notshown) which are required to perform the specified functions forimplementing the present invention, such as memory devices, interfacecircuits, D/A and A/D circuits, keyboard, display, speaker and so on.

[0140] Signal generator 60 also includes a frequency control circuit 67which provides an output signal to inverter 64 for controlling thefrequency of the signal provided to electrodes 11.

[0141] Footpedal 84 is provided with a switch 86 which is positioned tobe actuated by the surgeon. By closing switch 86 the surgeon commandsthe circuitry to commence a thermal cycle for bonding tissue.

[0142] The circuitry depicted in FIG. 15 can perform all of the varioustasks described above for tissue bonding in accordance with theinvention. As explained above, implementation of the invention requiresthe circuitry to operate in accordance with certain voltage, current andimpedance values. More specifically, as explained above, the voltage onelectrodes 11 rises at a predetermined rate during the first stage ofthe thermal cycle. This voltage increase is commanded by computercontrol system 70 (“computer”) via an output from microprocessor 72coupled to voltage regulator 62. Voltage sensor 65 measures the voltagelevel provided by voltage regulator 62, and provides it as feedback tomicroprocessor 72. If a discrepancy exists between the commanded voltageand the measured voltage, a suitable correction is made under computercontrol.

[0143] Thus, computer 70 controls the voltage and duration of the firststage. Operation of an analogous nature is provided to carry out thesecond stage in terms of controlling voltage and duration.

[0144] Current sensor 63 provides an instantaneous current measurementto computer 70. Since the voltage on electrodes 11 is computercontrolled, the current level is based on the tissue impedance. Thus,the tissue impedance can be calculated from the ratio of voltage tocurrent. In this way the computer 70 determines Z and Zo. Theseparameters are used by computer 70, in accordance with the descriptionprovided above, to control the thermal cycle.

[0145] The frequency of the HF signal provided to electrodes 11 is alsocontrolled by computer 70. The required frequency is outputted bymicroprocessor 72 and applied to frequency control circuit 67 whichdetermines the frequency generated by inverter 64.

[0146] The low frequency modulating signal is produced at the output ofpower supply 61 in accordance with voltage control signals generated bycomputer 70.

[0147] All of the components shown as blocks in FIG. 15 are well known.Obtaining such components and arranging them to operate with each otherin the manner described in detail herein is obvious to anyone withordinary skill in the art. Likewise, programming computer 70 to operatein the manner described herein is obvious to anyone with ordinary skillin the art.

[0148] As to computer 70, in its memory are stored the voltage, voltageincrease rate, frequency and other parameters predetermined byexperimentation to be effective to bond tissue of a particular thicknessand structure. The computer memory must contain data about bonding modesfor the tissues of various organs depending on the type of animal andits age. Examples of data stored in memory are set forth below inTable 1. TABLE I electrode work tissue surface thickness semi-compressed sleeve clamping voltage modulation two stage animal (approx.)electrode force rise rate voltage frequency frequency thermal cycleorgan microns) (microns) (N) (V/sec) (V) (kHz) (Hz) (time msec) Method 1110 ± 20 350 ± 50; 2.6 213 50 1000 150 + 1200 = rat dia 1550 1350abdominal aorta Method 2 110 ± 20 350 ± 50; 1.5 213 32 1000 0 150 + 400= rat dia 1550 550 abdominal aorta rat 25 ± 5 400 × 500 0.35 2207 341000 0 15 + 50 = epineurium 65 rabbit 50 + 25 = 350; 1.5 200 30 1000 0150 artery + 75 dia 1550 vein, Method 2 700 1 × 2 mm 3.5 start 300 (1)4550 6.0 150 + rabbit large 5.0 end 1200 intestine 700 1 × 2 mm 3.5 start267 (2)40 50 6.0 150 + 5.0 end 1400 rabbit liver 2.5 to 0 1 × 3 mm 4.5200 30 50 6.0 150 + 1200 rabbit gall 300 ± 50 0.5 × 2 mm 3.0 200 30 5060 150 + bladder 1200

[0149] Computer 70 must be provided with information to identify, forexample, the tissue type. Thus, the keyboard (not shown) can be used toenter “rabbit liver”. Other input data regarding tissue thickness,electrode work surface and clamping force is entered manually and/orautomatically by suitable devices. Once all of the input data has beenentered, computer 70 will generate corresponding output data to performthe thermal cycle, such as the voltage rise rate for the first stage,the voltage for the second stage, the high frequency, the modulationfrequency, the duration of both stages (in some embodiments), and so on.

[0150] The input data about the tissue which requires bonding is enteredinto the computer control system 70, output data is retrieved, and thethermal cycle commences at the surgeon's command. The output data can beautomatically corrected in correspondence with a control algorithm basedon feedback signals. Alternatively, system operation based on the outputdata retrieved from computer 70 can be corrected manually by thesurgeon's override according to the results he observes from the firstthermal bonding cycle.

[0151] Tools

[0152] The electrodes 11 must not only deliver current to the tissue,but to cool off its surface as well. Based on calculations andexperiments, it has been determined that the electrodes must be made ofmetal with a high heat conductivity. As between copper and stainlesssteel, for example, a temperature rise of 10° C. was measuredimmediately at the moment of bonding discontinuation at theelectrode/tissue interface for copper electrodes (heat conductivity 3.93W/cm C), whereas for stainless steel the rise was 25° C. (heatconductivity 0.162 W/cm C).

[0153] The volume of the electrode defines its heat capacity and, thus,its ability to function effectively as a heat sink and withstand severalsuccessive bonding cycles without becoming overheated. The electrodevolume Ve should be significantly larger than the volume of the tissueto be bonded. This is expressed by

Ve≈CS_(e)δ,

[0154] where

[0155] S_(e) is the area of electrode work surface,

[0156] δ is the thickness of flange 10, and

[0157] C is between 5 and 10.

[0158] The area size S_(e) of the electrode work surface is that portionwhich engages the tissue flange 10, and it defines the currentdistribution in the tissue contacted between the electrodes 11 and,hence, the distribution of heat generated by current flow within thetissue.

[0159] A demonstration of the electrode heat sink effect is depicted inFIGS. 13 and 14.

[0160] In FIG. 13 the temperature plotted is deep within the tissue,i.e. at the tissue/tissue boundary. It is assumed that the tissue haspoor heat conductivity and, therefore, for the short time between pulsesof power essentially no heat energy is lost. Therefore, the temperaturewill remain nearly constant.

[0161] However, FIG. 14 plots two temperatures, namely in tissue veryclose to the electrode (0.01 cm) and in tissue that is in contact withthe electrode. It is shown by the temperature drop between pulses thatthe electrode conducts heat away rapidly, even during that short timeperiod. Therefore, in the pulsed case for both tissue in contact withthe electrode and tissue only 0.01 cm away, the temperature willsignificantly drop even in the short time between pulses.

[0162] It has been discovered that another factor having a significanteffect on the heat generated in the tissue and the electrode/tissueinterface is the uniformity which is maintained in the area ofelectrode/tissue contact. The term “uniformity” in this context isdefined as being applicable to the nature of the contact (i.e. surfaceas opposed to point-by-point), perimeter of contact area, and thecurrent density distribution. Such uniformity is maintained by suitabledesign of the electrodes. In particular, the electrodes are shaped toform a contact area in accordance with a selected ratio between thelinear dimension of the contact area to thickness of the tissue. If theratio is low and the deformation of the bonded material is comparativelylow, the area of the highest heat generation is displaced toward theelectrode where the current density is the highest, whereas at thetissue/tissue interface the current density is lower. Therefore, bondingstarts in the wrong place (i.e. at the electrode/tissue interface) andonly later shifts over to the tissue/tissue interface where theanastomosis should be formed. The zone of the initial formation ofcoagulation overheats, and that causes sticking and has a negativeinfluence on the tissue healing process.

[0163] If the tissue deformation, or compression, is rather deep, thecurrent density at the tissue/tissue interface is higher and coagulationforms without zones of high “overcoagulation”.

[0164] In case of deep tissue deformation (approximately 50%) the ratioof the above-mentioned length dimension of the electrode to thethickness of the tissue layer should be not less than one. In theextreme case of low deformation (very hard tissue) this ratio must reach3.

[0165] A tool of such type is shown in FIGS. 16 and 17.

[0166] The arms 8 (see FIG. 1) are mounted into sleeve 100 and areconnected to contact pins 102 for connection to the HF power source 12.Electrodes 11 are soldered to the arms 8 in opposed relationship. One ofarms 8 has a lug 104 on the internal side of the arm. It is possible tolimit deformation of arms 8 and thus adjust the clamping force of theelectrodes on the tissue by replacing this part 104 with another of adifferent height.

[0167] When electrodes 11 come in contact there remains a gap betweenlug 104 and the opposite arm 8. Further deformation of the arms underthe pressure from the surgeon's fingers is limited by the lug andopposed arm coming in contact. The force of tissue compression by theelectrodes which is created during this action is expressed by theequation

P₁=aG

[0168] where

[0169] a is a gap between lug 105 and the surface of the opposed arm,and

[0170] G is a proportionality factor determined by the rigidity of thearms.

[0171] Further increase of pressure by the surgeon's fingers will notchange the compression force applied by the electrodes. The adjustmentof the forceps to the needed force P₁ is achieved by replacing part 104by a similar one but of a different height, or by means of changing thenumber of adjusting spacers 106 placed under lug 104.

[0172] When two thick layers of tissue are being bonded, each having athickness d, and these are placed between the electrodes, the clampingforce becomes

P ₂=(a+2dx)·G.

[0173] where x≈R/L, R is the distance from sleeve 100 to sleeve 104, andL is the length of arm 8 from sleeve 100 to electrodes 11.

[0174] The following ratio between the forces may be assumed:${\frac{P_{2}}{P_{1}} < 1.5},$

[0175] where $\frac{a + {2\quad d\quad x}}{a} < 1.5$

[0176] or

a>4dx

[0177] There is a knob 108 with a recess 109 for the operator's fingeron the external side of the arm. A strictly fixed location of theoperator's finger relative to the arm is an essential condition forcontrolling the clamping force on the tissue. A recessed spot for theoperator's finger makes manipulation easier, especially with a smallsize tool.

[0178] The main parameters that the tool is to meet are defined bytissue thickness d, bonding area S and specific pressure selecteddepending on the tissue type

arm flexure a>4dx

force P ₂ =S·p

[0179] rigidity $G = {\frac{P_{2}}{a + {2\quad d\quad x}}.}$

[0180] At a preset rigidity G, backlash is$A = {\frac{P_{2}}{G} - {2\quad d\quad {x.}}}$

[0181] Centralizer bar 110 is mounted into one of arms 8 through anelectric-insulating sleeve 112, and its other end enters hole 114 in theother arm 8.

[0182] Force P₂ is preset by selecting the thickness of adjustmentspacers 106.

[0183] All the free surfaces of the tool excluding the electrodes worksurfaces are covered with electric-insulating coating that preventspuncture at the electrical parameter values expected to be used, plus areasonable margin of safety.

[0184] A tool with two level settings of the clamping force using anelectromagnetic drive is depicted in FIGS. 18 and 19. The main principleof this tool is the same as in the one depicted in FIG. 16 in thatdeformation of arms 8 is limited in order to create the condition forsetting the force.

[0185] In this case, the deformation is limited not to one certain levelbut to two selectable levels.

[0186] For this purpose, an electromagnet, 116 is mounted on one of thearms 8, its armature 118 is connected with pin 120 that exits throughthe hole in stator 122.

[0187] Before the bonding is initiated the electromagnet is energized,the armature 118 is pulled toward stator 122 and the pin 120 is pulledout to its extended position. During the bonding process a signal tode-energize the electromagnet is sent from computer 78. Armature 118 isreleased and pin 122 is depressed. The deformation of arms 8 increasesunder pressure by the surgeon's fingers, providing the required increaseof the tissue clamping force. The initial and the final force is presetby selecting the length of pin 120 and lug 124, as well as the number ofspacers 106. Stator coil 122 is connected to a DC power source (notshown) through one of the pins 102 through which AC high frequencycurrent flows, and an additional pin 124 mounted into electric insulatedsleeve 100. The electric magnet is controlled by computer 78 whichcontrols the main power source 12.

[0188] Advantages of the invention have been found to include thefollowing:

[0189] the method is simple in usage, requires usual skills in generalsurgery on stomach, intestine, liver, gall and urine bladders and otherorgans;

[0190] the method is implemented with the help of forceps which is afamiliar instrument for surgeons, or with simple devices the usage ofwhich does not require special training;

[0191] tissues can be bonded layer-by-layer or in the mass, the weldingseam is neat and trim, leak-proof and reliable;

[0192] testing of the method on several types of animals (e.g. rabbits,white rats) proved its applicability in layer-by-layer closing ofwounds, stomach bonding “end-to-end” and “end-to-side”, reconstructionof stomach intactness, gall bladder and urine bladder surgery, and thisestablishes the wide applicability of the method and possibilities offurther extension of its clinical applications;

[0193] absence of complications in the post-operational period in 90% ofoperated-on animals that could be related to the method itself, ratherthan to improper use of anesthetic or technical errors by the surgeon;

[0194] the method reduces the duration of surgery by 50-60%, andfacilitates the surgeon's work;

[0195] typically, after having tried this method for the first time,surgeons master it without any difficulties and express an inclinationto continue deeper study of the method and introduce it into theirclinical practice.

[0196] The bond in tissue created by this invention has been describedherein in terms of the effect on albumin of heat generated by thecurrent passed through the tissue. It has been said that, when suitablyheated, the albumin joins the two edges of tissue to each other. This isone possible explanation. However, the physiological changes caused intissue by the present invention are not yet fully understood. It ispossible that physiological changes in addition to or in place of thealbumin effect occur due to the invention which contribute to thecreation of a bond.

[0197] Although specific embodiments of the present invention have beendescribed in detail, various modifications thereto will be readilyapparent to anyone with ordinary skill in the art. All suchmodifications are intended to fall within the scope of the presentinvention as defined by the following claims.

We claim:
 1. Apparatus for bonding soft biological tissue having anincision therein, comprising: forceps adapted to grip a portion of thetissue on both sides of the incision; electrodes adapted to contact saidtissue portion; an electrical power source for providing a highfrequency electrical signal to said electrodes to be passed through saidtissue portion; and control means coupled to said electrical powersource to provide said electrodes with one voltage signal during a firstof two stages, and another voltage signal during a second of said twostages.
 2. The apparatus of claim 1, wherein said control means controlsthe voltage signal of said first stage to have a varying level, and thevoltage signal of said second stage to have a constant level.
 3. Theapparatus of claim 2, wherein said control means provides a constantrate of increase in the voltage level of said voltage signal during saidfirst stage.
 4. The apparatus of claim 3, wherein said constant rate ofincrease begins at a voltage of zero.
 5. The apparatus of claim 3,wherein said constant rate of increase reaches a maximum voltage duringsaid first stage equal to said constant voltage level applied duringsaid second stage.
 6. The apparatus of claim 2, further comprising meansfor measuring impedance of said tissue portion, wherein said controlmeans controls duration of said first stage in response to said measuredimpedance.
 7. The apparatus of claim 6, wherein said control meanscontrols said constant voltage level of said signal during said secondstage based on said measured impedance.
 8. The apparatus of claim 7,wherein said control means controls duration of said second stage basedon said measured impedance.
 9. The apparatus of claim 2, furthercomprising means for measuring impedance of said tissue portion as afunction of time, means for detecting an impedance minimum of saidtissue portion after said first stage commences, wherein said controlmeans controls duration of said first stage in response to occurrence ofsaid impedance minimum.
 10. The apparatus of claim 9, wherein saidcontrol means controls said constant level of said signal based onoccurrence of said impedance minimum.
 11. The apparatus of claim 10,wherein said control means controls duration of said second stage basedon a comparison between a present value of tissue impedance and saidimpedance minimum.
 12. The apparatus of claim 1, wherein said tissueportion is in the form of a flange which includes joined edges of tissuefrom both sides of said incision and said electrodes engage oppositesides of said flange.
 13. The apparatus of claim 12, wherein the forcepsincludes clamping means for applying force to clamp the flange betweensaid electrodes to thereby compress said tissue portion.
 14. Theapparatus of claim 13, wherein said clamping means compresses saidflange during said first and second stages.
 15. The apparatus of claim14, wherein said clamping means continues to compress said flange for atime period after said second stage is completed.
 16. The apparatus ofclaim 15, wherein the clamping means increases said force during saidsecond stage.
 17. The apparatus of claim 13, wherein the clamping meanscontrols said force applied to said flange to a predetermined level. 18.The apparatus of claim 13, wherein said clamping means is mechanical.19. The apparatus of claim 13, wherein said clamping means iselectromagnetic.
 20. The apparatus of claim 1, wherein said power sourceprovides a frequency in the range of 50K to 2000K Hz.
 21. The apparatusof claim 1, wherein said control means modulates said constant voltagelevel during at least said second stage by a low frequency signal. 22.The apparatus of claim 20, wherein said low frequency signal is in therange of 4 to 6 HZ.
 23. Apparatus for bonding soft biological tissuehaving an incision therein, comprising: forceps adapted to grip aportion of the tissue on both sides of the incision; electrodes adaptedto contact said tissue portion; an electrical power source for providinga high frequency electrical signal to said electrodes to be passedthrough said tissue portion; and clamping means for applying force withsaid forceps to compress said tissue portion, said force being set todifferent levels in two time periods, respectively, while said highfrequency electrical signal is being passed through said tissue portion.24. The apparatus of claim 23, wherein said tissue portion is in theform of a flange which includes joined edges of tissue from both sidesof said incision.
 25. The apparatus of claim 24, wherein the level ofsaid force applied in a first of said two time periods is lower than thelevel of said force applied in a second of said two time periods. 26.The apparatus of claim 25, wherein the force level during said firsttime period is substantially constant.
 27. The apparatus of claim 26,wherein the force level during said second time period is substantiallyconstant.
 28. The apparatus of claim 27, wherein said second time periodfollows immediately after said first time period.
 29. The apparatus ofclaim 27, wherein said clamping means applies a force to said tissueportion after passing of said high frequency electrical signal throughsaid tissue portion is stopped.
 30. The apparatus of claim 29, furthercomprising a control means coupled to said electrical power source toprovide said electrodes with one voltage signal during a first of twostages, and with a different voltage signal during a second of said twostages.
 31. The apparatus of claim 30, wherein said first and secondtime periods correspond to said first and second stages, respectively.32. The apparatus of claim 23, wherein said clamping means applies aforce to said tissue portion after passing of said high frequencyelectrical signal through said tissue portion is stopped.
 33. Theapparatus of claim 23, further comprising a control means coupled tosaid electrical power source to provide said electrodes with one voltagesignal during a first of two stages, and with a different voltage signalduring a second of said two stages.
 34. The apparatus of claim 33,wherein said first and second time periods correspond to said first andsecond stages, respectively.
 35. Apparatus for bonding soft biologicaltissue having an incision therein, comprising: forceps adapted to grip aportion of the tissue on both sides of the incision; electrodes adaptedto contact said tissue portion; an electrical power source for providinga high frequency electrical signal to said electrodes to be passedthrough said tissue portion; and control means for providing a constantvoltage level of said signal during at least a portion of a time periodwhen said high frequency electrical energy is passed through said tissueportion, and for modulating said constant level by a low frequencysignal.
 36. The apparatus of claim 35, wherein the frequency of said lowfrequency signal is in the range of 4 to 6 HZ.
 37. The apparatus ofclaim 36, wherein the frequency of said high frequency signal is in therange of 50 kHz to 2000 kHz.
 38. The apparatus of claim 36, wherein saidlow frequency signal is a substantially square pulse.
 39. Apparatus forbonding soft biological tissue having an incision therein, comprising:forceps adapted to grip a portion of the tissue on both sides of theincision; electrodes secured to said forceps for contacting said tissueportion; an electrical power source for providing a high frequencyelectrical signal to said electrodes to be passed through said tissueportion; and wherein said electrodes are dimensioned relative to size ofsaid tissue portion to be an effective heat sink for conducting heataway from said tissue and thereby prevent sticking of tissue to saidelectrodes.
 40. The apparatus of claim 39, wherein said electrodes aredimensioned to have a volume which is at least 5 times that of thetissue portion volume.
 41. The apparatus of claim 40, wherein saidelectrodes are made of a metal with a high heat conductivity. 42.Apparatus for bonding soft biological tissue having an incision therein,comprising: forceps adapted to grip a portion of the tissue on bothsides of the incision; electrodes adapted to contact said tissueportion; an electrical power source for providing an electrical signalto said electrodes to be passed through said tissue portion; means forpredetermining impedance variation in said tissue portion as a functionof time while said electrical signal passes through said tissue portion,and to provide a preselected impedance value; means for measuringimpedance of said tissue portion to provide a measured impedance signalas a function of time while said electrical signal passes through saidtissue portion; and means for stopping said electrical signal from beingpassed through said tissue portion when a value of the measuredimpedance signal reaches a preset impedance value relative to saidpreselected impedance value, said preselected impedance value beingspecific in particular to the biological tissue being bonded.
 43. Theapparatus of claim 42, wherein said measuring means includes a voltagesensor, a current sensor and means to calculate a ratio therebetween.44. A method for bonding soft biological tissue having an incisiontherein, comprising the steps of: gripping a portion of the tissue onboth sides of the incision with forceps; contacting said tissue portionwith electrodes; providing a high frequency electrical signal to saidelectrodes to be passed through said tissue portion; and providing saidelectrodes with one voltage signal during a first of two stages, andanother voltage signal during a second of said two stages.
 45. A methodfor bonding soft biological tissue having an incision therein,comprising the steps of: gripping a portion of the tissue on both sidesof the incision with forceps; contacting said tissue portion withelectrodes; providing a high frequency electrical signal to saidelectrodes to be passed through said tissue portion; and applying forcewith said forceps to compress said tissue portion, said force being setto different levels in two time periods, respectively, while said highfrequency electrical signal is being passed through said tissue portion.46. A method for bonding soft biological tissue having an incisiontherein, comprising the steps of: gripping a portion of the tissue onboth sides of the incision with forceps; contacting said tissue portionwith electrodes; providing a high frequency electrical signal to saidelectrodes to be passed through said tissue portion; and providing aconstant voltage level of said signal during at least a portion of atime period when said high frequency electrical energy is passed throughsaid tissue portion, and modulating said constant level by a lowfrequency signal.
 47. A method for bonding soft biological tissue havingan incision therein, comprising the steps of: gripping a portion of thetissue on both sides of the incision with forceps; contacting saidtissue portion with electrodes; providing a high frequency electricalsignal to said electrodes to be passed through said tissue portion; anddimensioning said electrodes relative to size of said tissue portion tobe an effective heat sink for conducting heat away from said tissue andthereby prevent sticking of tissue to said electrodes.
 48. A method forbonding soft biological tissue having an incision therein, comprisingthe steps of: gripping a portion of the tissue on both sides of theincision with forceps; contacting said tissue portion with electrodes;providing an electrical signal to said electrodes to be passed throughsaid tissue portion; predetermining impedance variation in said tissueportion as a function of time while said electrical signal passesthrough said tissue portion, and providing a preselected impedancevalue; measuring impedance of said tissue portion to provide a measuredimpedance signal as a function of time while said electrical signalpasses through said tissue portion; and stopping said electrical signalfrom being passed through said tissue portion when a value of themeasured impedance signal reaches a preset impedance value relative tosaid preselected impedance value, said preselected impedance value beingspecific in particular to the biological tissue being bonded.
 49. Theapparatus of claim 1, wherein said electrodes are secured to saidforceps.
 50. The apparatus of claim 23, wherein said electrodes aresecured to said forceps.
 51. The apparatus of claim 35, wherein saidelectrodes are secured to said forceps.
 52. The apparatus of claim 42,wherein said electrodes are secured to said forceps.
 53. The apparatusof claim 42, wherein said preselected impedance value is substantially aminimum impedance.
 54. The method of claim 48, wherein said preselectedimpedance value is a substantially minimum impedance.
 55. The method ofclaim 42, further comprising means to store said preselected impedancevalue.
 56. The method of claim 42, wherein said stopping meanscalculates a ratio between said measured impedance signal and saidpreselected impedance value to determine when said preset impedancevalue is reached.
 57. The method of claim 48, further comprising thestep of storing said preselected impedance value.
 58. The method ofclaim 48, wherein said stopping step calculates a ratio between saidmeasured impedance signal and said preselected impedance value todetermine when said preset impedance value is reached.
 59. Apparatus forbonding soft biological tissue having an incision therein, comprising:forceps adapted to grip a portion of the tissue on both sides of theincision; electrodes adapted to contact said tissue portion in anelectrode/tissue contact area; an electrical power source for providinga high frequency electrical signal to said electrodes to be passedthrough said tissue portion; and wherein said electrodes are dimensionedrelative to size of said tissue portion to maintain uniformity in saidelectrode/tissue contact area.
 60. The apparatus of claim 59, whereinsaid electrodes are dimensioned such that a length of saidelectrode/tissue contact area is at least as large as a thickness ofsaid tissue portion.
 61. A method for bonding soft biological tissuehaving an incision therein, comprising the steps of: gripping a portionof the tissue on both sides of the incision with forceps; contactingsaid tissue portion with electrodes in an electrode/tissue contact area;providing a high frequency electrical signal to said electrodes to bepassed through said tissue portion; and dimensioning said electrodesrelative to size of said tissue portion to maintain uniformity in saidelectrode/tissue contact area.
 62. Apparatus for bonding soft biologicaltissue having an incision therein, comprising: forceps adapted to grip aportion of the tissue on both sides of the incision; electrodes adaptedto contact said tissue portion; an electrical power source for providingan electrical signal to said electrodes to be passed through said tissueportion; means for measuring impedance of said tissue portion as afunction of time while said electrical signal passes through said tissueportion; means for determining and storing a minimal value of tissueimpedance while said electrical signal passes through said tissueportion; means for determining a ratio of said measured tissue portionimpedance to said minimal value of tissue impedance while saidelectrical signal passes through said tissue portion after saidimpedance reaches its minimal value; and means for stopping saidelectrical signal from being passed through said tissue portion whensaid impedance ratio reaches a preset value, said preset value beingspecific for each bonded biological tissue.
 63. A method for bondingsoft biological tissue having an incision therein, comprising the stepsof: gripping a portion of the tissue on both sides of the incision withforceps; contacting said tissue portion with electrodes; providing agradually rising voltage to said electrodes for passing electric currentthrough said tissue portion, the rate of the voltage rise being specificfor each bonded biological tissue; measuring impedance of said tissueportion as a function of time while said voltage is provided to saidelectrodes; determining and storing a minimal value of said impedance;stabilizing the high frequency voltage at a level corresponding to saidminimal impedance value; determining a ratio of said measured tissueportion impedance to said minimal value; and stopping said highfrequency voltage from being passed through said electrodes when saidimpedance ratio reaches a preset value, said preset value being specificfor each bonded biological tissue.